The present invention relates to a linkage system for releasably latching a portion of an aircraft engine cowling to an engine casing, more particularly, such a linkage system for latching the portion of the aircraft engine cowling having a jet engine thrust reverser.
An aircraft jet engine power plant typically is enclosed by a cowling and is attached to the aircraft structure by a supporting strut. The cowling generally assumes the shape of a body of revolution about a longitudinal axis of the jet engine to provide aerodynamic airflow thereby minimizing the drag of the jet engine. The cowling may comprise several functional units, including a thrust reverser mounted to the rear of the jet engine. In order to minimize the weight of the cowling, it is typically fabricated from sheet metal and, even though stiffeners are incorporated into the cowling, it may deform during operation of the thrust reverser due to the high magnitude of forces imposed on the cowling.
In order to facilitate access to the jet engine, to the mechanical components of the thrust reverser and to make removal of the jet engine easier, the cowling, particularly the thrust reverser section, is designed in opposite C-shaped sections half clamshells along a vertical plane passing through the longitudinal axis of the jet engine. Typically, the half clamshells are pivotally attached to either the engine or the support strut structure enabling the two sections to be pivoted away from each other by moving the bottoms apart. The half clamshells are locked together at their displaceable ends when in their closed positions to form part of the engine cowling.
To decelerate the aircraft, the thrust reverser temporarily deflects at least a portion of the propellant gas flow toward an upstream direction and is thereby subjected to a large reaction force from the front towards the rear and extending generally parallel to the jet engine longitudinal axis. In order to prevent damage to the hinges linking the half clamshells of the thrust reverser to the support strut from this large reaction force and to preserve the half clamshells from stresses that may buckle the sheet metal, the half clamshells are also linked, when in their closed positions, to an outer casing of the jet engine by mutual engagement of two annular linkage elements, the engagement taking place in a plane extending substantially perpendicular to the longitudinal engine axis. The linkage element on the engine casing is stationary, while the engaging portion is attached to the inner side of the half clamshells. The stationary linkage element may have an annular notch, typically having a U- or V-shaped cross-sectional configuration in which the opening points radially outwardly away from the longitudinal axis of the engine. The engaging portions mounted on the half clamshells have shapes complimentary to the annular notch of the fixed linkage element and engage this notch when the half clamshells are in their closed positions.
Although in this known design, the axial reaction force is uniformly spread over the circumference of the external casing of the jet engine and of the half clamshells, the deformation of the cowling or any component thereof, in particular when subjected to centrifugal or radial forces, may lead to the disengagement of the movable linkage element from the notch and thereby separate the thrust reverser from the jet engine. Dynamic imbalance of the jet engine may also cause such a disengagement. The solution to this problem must be carried out without hampering the intentional opening of the half clamshells and without adding undue weight to the jet engine or to the cowling.